Backfire stop



M. P. WHITNEY BACKFIRE STOP March 10, 1936.

Filed Nov. 20, 1931 2 Sheets-Sheet 1 l/VVENTOR March 10, 1936. M WHITNEY2,033,565

' BACKFIRE STOP Filed Nov. 20, 1931 2 Sheets-Sheet 2 V I 5 JZ\ o 2 32 .9HIIIHMW 43 w //v VENTOR B Y M01209 1? A TTURNE Y Patented Mar. 10, 1936UNITED STATES PATENT OFFICE BACKFIRE STOP Application November 20, 1931,Serial No. 576,395

4 Claims.

This invention relates to a back-fire stop for internal combustionengines and more particularly to a device for preventing an internalcombustion engine from firing while it is rotating backwards.

Back-firing of internal combustion engines due to pre-ignition occurs insome installations due to failure of the operator to retard the ignitionduring starting, or due to the advanced setting of the ignition whensome forms of automatic spark advance are employed. It is, of course, ingeneral desirable to restrict such back-firing, and particularly inconnection with the use of automatic starting mechanism since if aseries of back-fires occur, as sometimes happens, the automatic startingmechanism may re-engage while the engine is rotating backwards, thussetting up heavy and possibly destructive stresses.

It is an object of the present invention to provide anovel device forstopping back-fire of internal combustion engines.

It is another object of the invention to provide such a device which iseffective to restrict back-firing to an initial explosion only.

A further object isto pro-vide such a device which is actuated by aninitial explosion to prevent the recurrence thereof.

Furtherobjects and advantages will be apparem to those skilled in thisart from the following description taken in connection with theaccompanying drawings in which:-

Fig. 1 is a semi-diagrammatic showing of a conventional type of internalcombustion engine with its ignition system illustrated in connectionwith one preferred embodiment of the invention;

Fig. 2 is an enlarged side elevation partly in section of an automaticswitch adapted. to operate in accordance with the present invention;

Fig. 3 is a similar view of the insulating cap of said switch;

Fig. 4 is a similar view of a modified form of said switch;

Fig. 5 is a similar View of the insulating cap thereof;

Fig. 6 is a similar view of the switch illustrated in Fig. 4 with theparts thereof moved to closed position;

Fig. 7 is a detail partly in section of an insulating guide thimble insaid switch;

Fig. 8 is an end view of the same; and

Fig. 9 is a semi-diagrammatic showing of an ignition system of aninternal combustion engine illustrated in connection with a secondembodiment of the invention.

Referring first to Fig. 1 of the drawings, there is illustrated aninternal combustion engine having a conventional form of ignition systemcomprising a battery I, grounded at 2 and arranged to be connected by anignition switch 3 with an ignition coil comprising a primary 4 and asecondary 5. The primary circuit is completed through a lead 6 to thebreaker mechanism 1 which is grounded at 8 and which is shunted by theusual condenser 9. Secondary 5 of the ignition coil is connected by alead I I to a distributor ll], mounted on the engine.

According to the present invention means are provided for rendering theignition system inoperative in response to backward rotation of theengine. As here illustrated, this device is in the form of a groundingswitch. l2 for the ignition system mounted on some portion of the fuelintake system of the engine such as the intake manifold l3, and arrangedto be operated by pressure generated within said intake manifold.

Referring now to Fig. 2 of the drawings, it will be seen that thegrounding device l2 comprises a metallic body portion l4 in the form ofa cylindrical casing provided with a threaded extension l5 adapted to bemounted in the intake manifold as shown in Fig. 1. A metallic pistonmember l6 forming one electrode of the switch is formed with acylindrical head I! adapted to slide in the cylindrical body I andhaving a substantially gas-tight fit therein. The stem N3 of the pistonmember is arranged to slide freely in an insulating guide member 19mounted within an insulating cap 2| and clamped thereby to the bodyportion I4 as by means of cooperating threads 22. The cap 2| carries astationary electrode 23 which is sealed in said cap in juxtaposition tothe end of the movable electrode l6 and protrudes therefrom to form abinding post as indicated at 24. Suitable yielding means such as aspring 25 is provided for normally maintaining the electrode l6 in theopen position as shown in Fig. 2, and vents 26 and 21 are provided inthe body portion l4 and cap 2! for permitting the escape of gas trappedback of the piston electrode whereby said electrode is permitted to movefreely to its closed position under the influence of pressure appliedthrough the passage 28 in the extension I5.

Means are preferably provided for delaying the return of the electrodeIE to its open position, and is here illustrated in the form of a ballcheck valve 29 arranged to seat against a shoulder 3| conformed theretoin the extension 15. It will be understood that the seat 3! is arrangednot to make a perfect gas-tight fit with said ball so that when thepressure is removed from the passage 28, gas will leak back past theball 29 and the piston 11 and gradually allow the electrode l6 to returnto its open circuit position.

In Figs. 4 to 6 inclusive there is illustrated a modified form of switchin which an insulating guide member 39 is provided which is perforatedas indicated at 4| to provide vents for the piston 42 leading to thevents 43 in the cap 44. It is thus unnecessary to vent the body portion45 of the switch. In this embodiment of the invention, no extraneousmeans are provided for returning the piston 42 to its open position, butreliance for this purpose is placed on the vacuum generated in theintake system during rotation of the engine by the starting motor andduring normal operation of the engine to move and return the pistonelectrode in its open position. In this embodiment of the invention, acheck valve 46 is illustrated which is similar to the ball check 29 ofFig. 2, but it will be understood that the employment of such delayingdevice is optional and it may be omitted if desired in order to providea more positive releasing operation for electrode 42.

Referring now again to Fig. 1 of the drawings, in the operation of thedevice, the grounding switch I2 is connected to ground the ignition leadII as by means of a lead 41. When the ignition switch 3 is closed andthe engine is rotated by the starting motor, the piston electrode E6 or42 is maintained in open position and the ignition functions in theusual manner. If, however, a back-fire should occur, a pressure isimmediately built up in the intake manifold I3 which causes the movableelectrode to slide to its closed position, as illustrated in Fig. 6.Connection is thereby established from the high tension lead ll throughthe lead 4?, fixed electrode 23, the movable electrode 16 or 42 and thebody of the switch Hi to the ground. The ignition is thus renderedinoperative and further back-fires are thereby prevented until thebackward rotation of the engine ceases and pressure in the intakemanifold I3 is dissipated.

An optional modification of the connection of the grounding switch tothe ignition system is illustrated in Fig. 9 which shows the groundingswitch l2 connected by a lead 48 to the primary lead 5 of the ignitioncircuit instead of to the secondary lead II as illustrated in Fig. 1.lhe remaining elements of this embodiment are similar to the partsillustrated in Fig. 1 and are similarly numbered. When this arrangementis used, closure of the switch l2 causes the primary circuit of theignition system to be grounded whereby said ignition is effectivelyrendered inoperative. Inasmuch as this period of inoperativeness is onlyof short duration, namely during the backward rotation of the engine, noharm will result to the ignition coil by reason of this temporary groundconnection.

Although certain forms and arrangements of the invention have been shownand described in detail, it will be understood that other embodimentsare possible and that various changes might be made in the details andforms of connection of the parts without departing from the spirit ofthe invention as defined in the claims appended hereto.

What is claimed is:

1. In combination with an internal combustion engine and an ignitionsystem therefor, means responsive to backward rotation of the engine forrendering said ignition system inoperative, said means being operativeto restore the ignition system to operative condition when backwardrotation of the engine ceases, and means for delaying such restorationto allow the engine to first come completely to rest.

2. In combination with an internal combustion engine having a fuelintake system and an ignition system therefor, means responsive topositive pressure in the intake system of the engine for grounding saidignition system for rendering the same inoperative until such intakepressure is dissipated, and means for thereupon returning said ignitionsystem to operative condition.

3. In combination with an internal combustion engine having a fuelintake system and an ignition system therefor, means responsive topositive pressure in the intake system of the engine for rendering saidignition system inoperative and means for retarding the release of suchpressure from said pressure responsive means.

4. In combination with an internal combustion engine having a fuelintakesystem and an ignition system therefor, grounding means for saidignition system including a fixed contact, a movable contact, meansresponsive to positive pressure in the intake system of the engine forclosing said contacts, and means for retardingv the release of thepressure from said pressure responsive means.

MAURICE P. WHITNEY.

